1. Field of the Invention
This invention relates to levels and, more particularly, to an electronic level apparatus and method whereby an audible tone is produced to indicate whenever the level is in a predetermined position.
2. The Prior Art
Various forms of levels have been used throughout history as devices to enable the operator to determine when a particular surface is horizontal. Early levels consisted of a body of liquid in an open vessel since liquid is known to form a flat, horizontal surface. The surface of the liquid formed a reference surface which served as the standard against which the horizontal character of a second surface was estimated. This basic principle has evolved into a bubble level wherein a bubble is trapped in a body of liquid, the liquid being enclosed in a upwardly curved, clear tube. The tube is oriented in the level apparatus so that the curvilinear orientation of the tube is in the vertical plane to thereby place the bubble in the center of the tube when the level corresponds with the horizontal. Centering marks are generally included on each side of the leveled bubble to more accurately indicate when the horizontal position has been achieved with the level. An accurate vertical positioning of an object perpendicular to the horizontal can be achieved by placing a second tube in the level so that the bubble in the second tube is centered when the level is perpendicular to the horizontal.
Clearly, this type of leveling device depends entirely upon the user being able to visually observe the respective bubble in order to accurately determine either the horizontal or vertical position of the level. However, there are many circumstances where it is impossible to visually observe the correct bubble position either by reason of its physical location or the lack of sufficient light. Other applications lend themselves to sensing the orientation of an object electronically. Several patents disclose various methods of accomplishing this result.
Conrad (U.S. Pat. No. 3,184,861) discloses a position deviation sensing device utilizing skin effect on a liquid electrolyte encapsulated within a nonmagnetic material.
Scopacasa (U.S. Pat. No. 3,786,472) discloses an electric level which uses movement of an electrically conductive liquid contained in a suitably sealed chamber. Electrodes are embedded in the chamber and correspond to points of contact of the liquid when the chamber is inclined to predetermined angles.
Chaney (U.S. Pat. No. 3,984,918) discloses an inclinometer that uses a ferrofluid enclosed within a torroidal chamber. The ferrofluid is carried in a closed planar loop which is symmetrical about at least one axis. Inclination of the loop in the plane in which it lies causes relative displacement of the liquid and the loop. The displacement of the ferrofluid in the loop is sensed electronically.
Cantarella, et al. (U.S. Pat. No. 4,167,818) discloses an electronic inclination gauge wherein a digital readout is provided by a gravity-sensitive potentiometer. The potentiometer is in the form of a sealed, circular cell partially filled with a semiconductive liquid such as alcohol. Electrodes are emerged in the alcohol and serve as the sensors for sensing the position of the alcohol in the cell.
Kent, et al. (U.S. Pat. No. 4,672,753) discloses a rotation sensor wherein a torroidal chamber having a square or rectangular cross-section contains a small body of dielectric or resistive fluid which has a total volume less than a 30.degree. sector of the channel. A discontinuous resistive strip circles the interior surface of the channel outer wall and a continuous conductive strip circles the exterior surface of the channel inner wall.
Clearly, numerous devices are available to allow the operator to either visually or audibly check the orientation of a particular surface. Therefore, what is needed is a level apparatus that can be selectively preset to a specific angle of inclination ranging between the horizontal and the vertical and having an audible signal means to audibly signal when the level is oriented at the specifically selected angle. Such a novel apparatus and method is disclosed and claimed herein.